In order to realize a highly-integrated semiconductor device, it may be necessary to have a method of forming fine patterns. For example, to integrate more and more devices in a given area, a size of each pattern should be as small as possible. In other words, patterns should be formed in such a way that a pitch thereof or a sum of a width of each pattern and a space between adjacent two of the patterns is reduced. However, as semiconductor device design rules are drastically reducing, resolution in a photolithography process is being stretched to the limit, and thus, it becomes more and more difficult to form patterns having a fine pitch.